Phosphorylation of riboflavin



Patented Sept. 9, 1952 J'PHOSPHORYLATION OF, RIBOFLAVIN Leo A. Flexser, Upper Montclair,; and Walter G. .IFarkas, Nutley, N. J., assignors toHoffmann- La Roche Inc., Nutley, N. J.

l 1N0 Dra in 1 Appli ptember 2.811951, Serial No. 248,869

18 Claims. (01.- zen-211.5)

I his invention is concerned with thenovel preparation of a physiologically active monophosphoric acid esterof ribofiavin'. This ester, especially in the form of itssalts, e. g., its sodiumsalt, has the veryawdesirable property of. being .much more soluble than riboflavin itself .and is,. there- -fore, of great utility tor the preparation ofpsolu- "tions of riboflavin suitablefor injection or incor- -'poration-into foodse: Unlike riboflavinesters of h organic :acids, our-monophosphoric acid ester also -hasthe great advantage of. being strongly re- -*sistantto .-hydrolysis over awiderange oipH.

Our invention also embracesnew:intermediates for producing that ester.

This application is-acontinuation-impart of our applications. Na141,585,,filedJanuary 31, 1950.

lbw-Kuhn and-his co-workers (Ber. 69, .1543, i -1974 (1936) U. S. Pat. 2,111,491) reportedethe preparation of a-ribofiavin phosphoric acid ester ":but did not state themelting point orwoptical ro- ---tation of their product. P. .Karrer and his cof workers (Helv; ChimwActa 20,= 79 t-(1937)), at-

tempting to repeat thework of Kuhnet all stated the following (p. 81): ,We have tried dozens of experiments but did notsucceed thus far in ob- --taining pure synthetic lactoflavin :(riboflavin) phos'phoric? acid. On the contrary; the: composition of thew preparations was always. variable and did notrconform to that of a=simple calcium salt of- 1actoflavin phosphoric acid: It may be assumed that-the authors quoted (Kuhn et a1.) encountered similar difficulties since they do not publish-analytical figures about their preparation (whereaswtheydo so for theinphosphorus-free intermediate products) The process set forth in." the above mentioned Kuhnpatentzis represented in that-patent to involve a reactionbetween riboflavin: sand .phosphorus x'oxychloride. The purported reaction is "stated-to take place in qthe; presence .of an ;.organic base and, moreparticularly, inq-the presence of ipyridinewThe use f phosphorusvoxyhalide, as

- set forth inthat patent qhasi howeverpnot proven W'SllOCeSSfuL as' note the; observations of P.;Karrer and .his -co-workers, supran We: havetriepeated the Kuhn process usingthe specific phosphorus oxyhalide mentioned the patent, namely, phosf phorus oxychloride", in the' presence of pyridine, and-havenotbeen ableto establish the synthesis of thedesired' monophosphoric acid ester of ribofiavin that process. As will be shown'hereinafter) our pr-oce'ss involves a-distinct departure ro'mthe Kuhn process in that we' do notemploy 1 phos horusoxyhalide, but on the contrary, W

- use certain monoand di-halophosphoric; acids,

namely,- monoand di-chlorophosphoric acids,

monoand di-brorriophosphoric acids, andlmonoand di-fluorophosphoric acids. I r

Our novel processior phosphorylating riboflavin, in contradistinction to that of Kuhn et al., offers no difficulties and produces a readily isolable riboflavin monophosphoric acid ester in good yield.

Afurther advantage of our invention is .thatjno base, such as-pyridine, is required to catalyzethe phosphorylation, as is usedbyKuhn et al nor is it necessary to maintain rigidly anhydrous conditionsusually needed with a POClr-pyridine-phosphorylating mixture. :1

Our process comprises reactingvriboflavin with a halophosphoric acid represented byithetformulae (HO)2POX and HOPOXz, wherein X is a halogen selected from the group consisting of chlorine, bromine and fluorine:Whenrseveral volumes of an anhydrous ether, e. g., ethyl ether or isopropyl ether, are added to the solutionobtained after reaction of. riboflavin with a halophosphoric acid, according to our invention, a solid is precipitatedwhich may be filtered, washed with the ether anddried.

Preferablythe reaction isicarriedhout with a great excess ofphosphorylating agent andfor a sufficient length of time to insure that no riboflavin remains unphosphorylated. The products which are thereupon obtained containrphosphorus and a halogen; The extent of the'phosphorylation dependsion the length of time theribofiavin is allowed'to .reactswith the halophosporictacids.

The extent ofipho'sphorylation is'imm-ateriaLas in all: cases the phosphorylated products, 'uponhy drolysis, yield :ribofiavin. monophosphoric, acid esteras a:final p'rcductg" While the mainproduct is' ribflaxin-5':monophosphoric1 acid jester, a minorportion of riboflavin -(2'),-(3"), 0n-(4) monophosphoric acid. ester may also be formed.

ltcis to be understood that we do notwish to limit ourselves by any theoretical" interpretation of the formation of our new riboflavin compounds containingphosphorus and a halogen. The reac- -tioninvo1ves. formation of halogenrcontaining phosphorylated products. Howevenwe dof not Wwish to limit our invention to any specific theory of. reaction or structure of products. Whilethe aforementioned phosphorylated halogen contlaining intermediates may bei-isolatedre. l, bypre- 1 cipitationwith ether, it is not necessary toleffect suchisolation for the preparation of riboflavin monoph osphoric, acid 3 ester. the "latter" instance, the reaction mixture afterphosphorylation of the riboflavin by the halopho sphoric acid molel o'f water.

then readily isolated from the solution, e. g., by

ry'stallizatic'iri. I g

The halophosphoric acids may be prepared by treating a phosphorus oxyhalide (PQXe) wherein X'stands for chlorine, bromine, or fluorine, with water. Riboflavin is soluble in and is readily phosphorylated by these agents at room temperature. The formation of the I'Iionohalophosphoric acids" and dihalophosphoric acids used in our process is shown hereinafter as occurring by re-' action between phosphorus oxyhalide and water.

' We prefer to employ about 1 to 2 molesof water per rrio'leof phosphorus oxyhalide. The treatin'ent of phosphorus oxyhalide with water follows the course:

X representing chlorine,- bromine or fluorine.

The fluorophosphoric acids can' also be" prepared by the method of U. s. Patent No. 2,423,895. The analogous chloro and bromo acids can similarly be prepared by this method. The chlorophosphoric, bromophosphoric and fluorophosphoric acids can, of course, be formed in the presence of riboflavin and thus react directly with the a be restrictive of the scope of our invention.

EXAMPLE i To 611.3 g. or phosphorus" oxychloride (0.4 mole) were added slowly, with good agitation and with cooling to about room temperature,- 7.2 g. (0.4 The mixture was stirred until evolution" of hydrogen chloride gas appeared mostly finished and allowed to stand overnight. The mixture was then cooled to 5 C. and 3.76 g. riboflavin added-with stirring. Complete solution took place quickly and H01 was evolved. The solution was kept at 5 C. for 1 /2 hours and then at room temperature for 3 hours. The solution was added slowly and with stirring to about 500 :c. anhydrous ethyl ether. The yellow precipitate which formed was filtered off, washed thoroughly with ether and dried in vacuo. Weight:5.5 g. Analysis showed a content of 2.4 atoms phos- It decomposed at EXAMPLE 2 The product of Example 1 was hydrolyzed by adding it to 100 cc. of water. A clear amber solution was obtained from which riboflavin mono phosphoric acid ester crystallized in hexagonal plates. The mixture Was allowed to stand overnight to complete the crystallization. It was then filtered, washed with alcohol and ether and dried.

' The yellow product melted at about 195 C. and

analyzed correctly for the monophosphoric acid ester of riboflavin corresponding to the formula Q 'C17H19N406PO3H2. The optical rotation of a 2 percent solution in concentrated hydrochloric acid was [ol :+44.5. On potcntiometric titration with sodium hydroxide, a well defined pbint of inflection in the titration curveftas obtained at? pH 4.5 upon the addition of exa'c y o'ri'e-equiva lent of alkali. A second inflection 't'at pri sfifi was obtained upon the addition of a second equiv-' alent of alkali. The substance resem ed riboflavin in appearance. had biological acti ty, but 1 was easily distinguishable by its greater iwater' solubility, the fact that it gelled somewhatfupon. addition to water, and by its formation of highiy" water-soluble salts with alkali hydroxides, aim monia, diethanolamine and the like.

EXAMPLE 3 14.4 g. (0.6 mole) of water were added to 61.3 g. (0.4 mole) of phosphorus oxychloride as in Example 1 and the mixture allowed to stand overnight. 3.76 g. riboflavin were added with stirring, rapid solution being obtained with evolution of H6 1 gas. The solution was allowed to stand at room temperature for 65 hours and then slowly added to 500 cc. anhydrous ether. A redbrown precipitate was obtained which was filtered, washed with ether and dried in vacuo. The product weighed 6.2 g'., indicating greater polyphosphorylation than in Example 1. This product was added to 62 cc. of dioxane containing 6 dc. of wat'er. Solution took place, followed-by crystallization of riboflavin monophosphoric acid ester. The latter substance was filtered the following da'y, washed with dioxane and ether and dried. Its properties were similar to those of the product of Example 2.

3.76 g. riboflavin were reacted with 61.3 g. phosphorus oxychloride pretreated with 7.2 g. water exactly as in Example I. The reaction solution then was poured into a mixture of 200 g. ice and 200 g. water and allowed to stand overnight. Riboflavin monophosphoric acid ester crystallized. It was filtered off, washed with 3 N hydrochloric acid, alcohol, ether and dried. The prodnot was similar to that of Example 2.

EXAMPLE 5 I To 63.5 g'. (40 cc.) of difluorophosphoric acid [HOPOFz] were added 7.52 g. of riboflavin with stirring and cooling to about room temperature. The riboflavin went slowly into solution, and a pasty yellow precipitate appeared after 20 minutes. Another 25 cc. of difluorophosphoric acid were added and stirring was continued for 2 hours at room temperature. The viscous slurry was then cooled in an ice bath and 400 cc. of anhydrous ethyl ether were added. The resulting yellow precipitate was filtered off, washed thoroughly with ether and dried in vacuo. at room temperature. It weighed 9.0 g. The product was hydrolyzed by dissolving 6 g. in 10 cc. of concentrated hydrochloric acid and adding cc. of water to the clear solution. The monophosphoric acid ester of riboflavin began to crystallize. After standing for two hours, the crystals were filtered ofi, washed with 30 cc. of normal hydrochloric acid, alcohol and ether and dried.

EXAMPLE 6 7.52 g. (0.02 mole) of riboflavin were added with stirring to 40 cc. of monofluorophosphoric acid [(l-IO)zPOF] and the reaction mixture was cooled in a water bath to room temperature. Complete solution was obtained in about five minutes. After 30 minutes a yellow precipitate formed. After 90 minutes total reaction time, 500 cc. of isopropyl other were added slowly with bromide wane;

were slowly added with stirring and cooling to aboutfroom temperature. Hydrogen bromide was voltd and solutior'fwas obtained after about 30 minutes. fitirring was continued for another hour and "the-soluti'o "was-alien allowed to stand i for about I "lfi hoursw There were then added 7.52 g. of riboflavin with stirringi Hydrogen bromide-was evolved and a solution was rapidly obtainedf 'lhereactiorrwas allowed toproceed for -'30 minutes, the solution was the of-f anhydrous -ether were dded. precipitatewhichfortified wasiiltered o well with ether and' dried in 'vacuo at room temperature. The product weighed 12.45 g., Eight I grams of the productfwer dissolved m 5 to. of concentrated "hydrochloric acid. The" "solution was clarified by filtration and 220 cc. of water were added. Riboflavin monophosphoric acid ester crystallized. The slurry was allowed to stand for about 16 hours, and the yellow precipitate was then filtered off and washed with 30 cc. of normal hydrochloric acid, alcohol and ether and dried. The product thus obtained was the monophosphoric acid ester of riboflavin.

EXAMPLE 8 To 114.5 g. -(0.4 mole) of phosphorus oxybromide, 14.4 cc. (0.8 mole) of water were slowly added with stirring and cooling to room tem perature. Hydrogen bromide was evolved. Stirring was continued for 90 minutes and the solution was allowed to stand about 20 hours to complete the reaction. 7.52 g. (0.02 mole) of riboflavin were added to the solution with stirring. After 90 minutes, 500 cc. of isopropyl ether were added with stirrin and cooling to about room temperature. The resulting precipitate was filtered, washed well with isopropyl ether and dried in vacuo. The resulting brown solid was dissolved in cc. of concentrated hydrochloric acid and 90 cc. of water were added to the solution. Precipitation started and the mixture was allowed to stand for about hours. The product was then filtered oif, washed with cc. of normal hydrochloric acid, ethyl alcohol and ether, and dried. The product thus obtained was monophosphoric acid ester of riboflavin.

EXAMPLE 9 As a further illustration of a phosphorylating procedure, the following is set forth. 61.3 g. (0.4 mole) phosphorus oxychloride were added slowly to 19.6 g. (0.2 mole) of orthophosphoric acid with agitation and cooling to room temperature. To the mixture, after standing overnight, 7.52 g. of riboflavin were added with stirring. Solution occurred after a short time. The reaction was allowed to proceed for 8 hours at room temperature. The clear red solution was 9 fii i tisi i.f-i ie i a.i s? :l. .fil ql i r $3. 511,9 29; eefil i at me ee e esaring e eqe s r eee rmo ph h acid ester isgiven as follows: 1 V

Preparatiofi o'rmmioscamarwazt dfiwrbtyiavm monophosphorz'c acid ester 4.56 g. of riboflavin monophosphoric acid ester are suspended in about 100 cc. of water and the pH brought to 4.5 by addition of one or two normal sodium hydroxide. Practically all of the 40 ester will dissolve upon continued stirring and crushing of the gelled portions. Opalescence, if present, may be removed by filtration through a fine sintered glass filter. The solution may also be clarified by addition of a small amountof niacinamide or gentisic acid ethanolamide or by bringing the pH to 9 by addition of NaOH followed by addition of glacial acetic acid to pH 4.5. Having obtained a clear solution at pH 4.5, about five volumes of ethanol are added, resulting in the precipitation of the monosodium salt of riboflavin monophosphoric acid ester. This is filtered oil", washed with ethanol and ether and dried in vacuo at 50 C. The product is a yellow powder weighing about 4 g. It gives a clear aqueous solution at a concentration of 25 nag/cc.

We claim:

1. A process of phosphorylating riboflavin which comprises reacting riboflavin with a member selected from the group consisting of the acids represented by the formulae (HO)2POX and HOPOX2, wherein X is a halogen selected from the group consisting of chlorine, bromine, and fluorine. v

2. A halogen-containing product produced abcording to the process of claim 1.

3. A process of phosphorylating riboflavin which comprises reacting riboflavin with the acid represented by the formula (HO)2P0C1.

4. A chlorine-containing product produced according to the process of claim 3,

5. A process of phosphorylating riboflavin which comprises reacting riboflavin with the acid represented by the formula HOPOClz.

6. A chlorine-containing product produced according to the process of claim 5.

7.A process of phosphorylating riboflavin jowhi'ch comprises reacting riboflavin with the acid represented by the formula (HO)2POB1'.

8; A bromine-containing product produced according to the process of claim 7.

l 16. A process of phosphorylating riboflavin which comprises reacting riboflavin with the acid I represented by the formula (HO)2POBr, and hydrolyzing the reaction product to produce ribo 9. A process of phosphorylating riboflavin"- which comprises reacting'riboflavin with theacid represented by the formula HOPO-Brz.

10. A bromine-containing product produced according to the process of claim 9.

11. A process of phosphorylating riboflavin which comprises reacting riboflavin with the acid represented by the formula (HO)2POF.

12. A fluorine-containing product produced according to the process of claim 11.

13. A process of phosphorylating riboflavin which comprises reacting riboflavin with a memacids represented by the formulae (HOMPOX and HOPOX2, and hydrolyzing the reaction product to produce riboflavin monophosphoric acid ester, wherein X is a halogen selected from the group consisting of chlorine, bromine, and fluorine.

14. A process of phosphorylating riboflavin which comprises reacting riboflavin with the ber selected from the group consisting of the acid represented by the formula (HO)2POC1,

and hydrolyzingthe reaction product to produce riboflavin-5-monophosphoric acid ester.

15. A process of phosphorylating riboflavin which comprises reacting riboflavin with the acid represented by the formula HOPOClz, and hydrolyzing the reaction product to produce riboflavin-5'-monophosphoric acid ester.

, flavin-5-monophosphoric acid ester.

17 A process of phosphorylating riboflavin which comprises reacting riboflavin with the acid represented by the formula HOPOBrz, and hydrolyzing the reaction product to produce riboflavin-5-monophosphoric acid ester- 18. A process of phosphorylating. riboflavin which comprises reacting riboflavin with the acid represented by the formula (HOMPOF, and hydrolyzing the reaction product to produce riboflavin-5-monophosphoric acid ester.

LEO A. FLEXSER. WALTER G. FARKAS.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date Number Name 2,024,036 Funaoka Dec. 10, 1935 2,111,491 Kuhn 1 Mar. 15, 1938 2,535,385 Breivogel Dec.'26, 1950 FOREIGN PATENTS Number Country Date Switzerland Aug. 16, 1937 

1. A PROCESS OF PHOSPHORYLATING RIBOFLAVIN WHICH COMPRISES REACTING RIBOFLAVIN WITH A MEMBER SELECTED FROM THE GROUP CONSISTING OF THE ACIDS REPRESENTED BY THE FORMULAE (HO)2POX AND HOPOX2, WHEREIN X IS A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORINE, BROMINE, AND FLUORINE. 